Opto-switches (also referred to as opto-isolators or optocouplers) use a short optical transmission path to transfer a signal between elements of a circuit while keeping the elements electrically isolated. They are used in medical devices to prevent current leakage from the circuits of the device to the patient's body. Opto-switches are supposed to be effectively leakage-free even under high voltage. If an opto-switch fails, however, it may permit high leakage current to reach the patient. When the leakage current flows through a cardiac catheter, for example, the consequences can be fatal.